The present invention relates generally to a godet roll for guiding, heating and conveying yarn. More particularly, the present invention relates to such a godet roll comprising a projecting support, a drivable hollow-cylindrical godet roll casing forming a circumferential yarn guiding surface, at least one radially acting bearing rotatably seating the godet roll casing on the projecting support in at least one bearing plane, the radially acting bearing comprising a plurality of bearing pole windings, and a heating device comprising a plurality of heating pole windings on the support, the bearing pole windings and the heating pole windings being arranged within an annular chamber between the support and the godet roll casing.
A godet roll of the above-described type to which the invention relates is disclosed in European Patent Publication EP 0 770 719 B1. This known godet roll heats a rotatably seated godet roll casing, on the circumference of which one or more yarns are guided. The godet roll casing is embodied to be cylindrical and hollow and is seated by means of several magnetic bearings on a projecting support. In addition to the magnetic bearings, a heating device for heating the godet roll casing is arranged in an annular chamber formed between the support and the godet roll casing. Basically, two problems occur with this arrangement, which considerably hamper the function of the godet roll. First, the godet roll casing is only insufficiently heated in the area of the magnetic bearings, such that the yarn or yarns can be guided only in the center area of the godet roll casing in order to receive a thermal treatment of the yarn or yarns.
A further problem is caused by the arrangement of the sensors of the magnetic bearings provided within the annular space for detecting the position of the godet roll casing. With the godet rolls customarily used conventionally, temperatures of approximately 230 degrees Celsius prevail in the interior of the godet roll casing, which directly affect the sensors. Since the magnetic seating requires a very exact determination of the seating of the godet roll casing, and therefore requires very sensitive sensors which, however, can hardly tolerate these high temperatures, a dependable detection of the seating of the godet roll casing, and therefore exact seating by means of the magnetic bearings, is not assured.
It is therefore a basic object of the present invention to provide an improved godet roll of the type described above and, more particularly, to provide a godet roll wherein uniform heating of the godet roll casing is possible without a deleterious effect on the magnetic seating of the godet roll casing. It is a further object of the present invention to enable the detection of the position of the godet roll casing essentially unaffected by the heating device.
In accordance with the present invention, these objects are addressed by providing a godet roll wherein at least one of the heating pole windings is arranged in a bearing plane between the bearing pole windings of the bearing plane and wherein a plurality of sensors are provided outside the annular chamber for determining the position of the godet roll casing and are connected with a control device for controlling the bearing pole windings.
Such a godet roll of the present invention is particularly distinguished in that the bearing areas of the godet roll casing can be directly heated. At least one of the heating pole windings is arranged in one of the bearing planes between the bearing pole windings of the bearing plane for this purpose. A bearing plane is defined as that normal plane of the godet roll in which the bearing pole windings are arranged. Therefore, the godet roll casing is not only radially supported in the bearing plane, but is simultaneously heated by the current generated by the heating pole winding. In such case, the air gap set between the heating pole windings and the godet roll casing is a function of the bearing gap controlled between the bearing pole windings and the godet roll casing. Therefore, the combination of the present invention allows the setting of the smallest air gaps, so that a loss-resistant heating of the godet roll casing is possible. The heating pole windings, as well as the bearing pole windings, can act in the same or in opposite directions. When acting in the same direction, the air gap and the bearing gap are formed between the pole ends and the godet roll casing. When acting in the opposite direction, the air gap is formed between the godet roll casing and the pole ends of the heating windings, and the bearing gap is formed between a hub or shaft and the pole ends of the bearing windings.
A further feature of the present invention is particularly advantageous for obtaining a seating of the godet roll casing which is as rigid and vibration-free as possible, and therefore an air gap between the heating pole windings and the godet roll casing extends uniformly over the entire length of the godet roll casing. According to this feature of the invention, the bearing pole windings of the magnetic bearing are distributed over at least three bearing planes, with at least some of the heating pole windings of the heating device being provided in the bearing planes between the bearing pole windings. A distribution of the bearing pole windings over several bearing planes has the advantage that a flat seating, and therefore a flat support of the godet roll casing, is achieved. Thus, the distribution of the bearing pole windings and the heating pole windings over the support provides for a uniform distribution of the positions at which a force is introduced for the radial seating of the godet roll casing, as well as induced currents for heating the godet roll casing. Thus, the tendency of the godet roll to become deformed at high speeds, for example to bend in case of sympathetic vibrations, is reduced by the flat seating of the godet roll casing.
In accordance with another advantageous development of the invention, the heating pole bearings and/or the bearing pole windings can be distributed over a support at offsets relative to each other from one bearing plane to another bearing plane. In case of such an angular offset arrangement of two pole windings, the angular position of a second pole winding in a second bearing plane is differentiated from a first bearing winding in a first bearing plane. The angular position of a pole winding is the position of the pole winding at the circumference of the support. If a position perpendicularly above the axis of rotation is selected as the reference position, the angular positions perpendicularly below the axis of rotation are 180 degrees spaced therefrom, and those of the lateral position on the level of the axis of rotation are 90 degrees and 270 degrees spaced therefrom.
With an angularly offset arrangement of the bearing pole windings, the directions from which a force is exerted on the godet roll casing vary. This arrangement makes possible a radial seating of the godet roll casing with an arrangement of only one or two bearing pole windings in one bearing plane, so that a relative large installation space for receiving the heating pole windings is available in the bearing plane. In the process, the bearing pole windings of different bearing planes cooperate.
In accordance with another aspect of the present invention, a spirally-shaped arrangement of at least some heating pole windings and/or bearing pole windings from one bearing plane to the next achieves further uniformity in the distribution of the bearing pole windings on the support. In this connection, it is also possible to combine the heating pole windings of one bearing plane in a common heating zone. In such case, the godet roll casing would be divided in the axial direction into a plurality of heating zones, such that each one of the heating zones can be heated by at least one, or several, heating pole windings.
However, it is also possible to arrange the heating pole windings and/or the bearing pole windings overlappingly in the circumferential direction of the support. In this manner, it is possible to achieve a uniform and large energy density, particularly for heating the godet roll casing.
The provision of the godet roll of the present invention with several sensors arranged outside of the annular space for determining the position of the godet roll casing, so that no thermal overload of the sensors can occur, represents a further attainment of the basic object of the invention. The sensors are coupled with a control device which controls the bearing pole windings. In such case, the sensors can be positioned at locations at which the surroundings permit a sensitive position measurement in every operating range. It is presumed that the bearing gap changes occurring between the bearing pole windings and the godet roll casing are propagated to each position connected with the godet roll casing because of the rigidity of the godet roll casing.
According to a particularly preferred further development of the invention, the sensors are arranged in the area of the bearing planes, wherein air gaps are formed between the godet roll casing and the support in the area of the bearing planes outside of the annular gap, with the bearing planes being essentially parallel in respect to a bearing gap formed between the godet roll casing and the pole ends of the bearing pole windings. Here, the sensors for monitoring the air gaps are embodied as distance sensors. This arrangement allows a very sensitive and delicate position determination, which assures the exact control of the magnetic bearings.
In such an embodiment, the air gaps can be formed, on the one hand, on a free end of the support inside the godet roll casing between a hub connected with the godet roll casing or, on the other hand, on the clamped end of the support outside of the godet roll casing between the godet roll casing and a collar connected with the support. In this manner, the position of the godet roll casing can be determined at both ends, so that an alignment by means of the magnetic bearing is assured.
A particularly advantageous further development of the invention provides for a sensor to be assigned to each bearing pole winding, such that the bearing pole windings are each separately controllable by means of the control device. This embodiment is particularly advantageous with an arrangement of individual bearing pole windings in individual bearing planes for the possible arrangement of several heating pole windings in the bearing planes.
However, it is also possible to control the bearing pole windings in pairs by means of the control device. In this case, a pair of bearing pole windings can be arranged in one or in two bearing planes.
In another embodiment, the godet roll casing is seated by means of an additional axial bearing for absorbing the axial forces. The axial bearing is preferably designed as an axially acting magnetic bearing. However, it is also possible to constitute the axial bearing by means of rolling bearings of an axial or radial design.
To assure the emergency running of the godet roll casing, at least one catch bearing is provided, which can be embodied as a contactless radial bearing or a resiliently connected radial bearing.
Exemplary embodiments of the godet roll in accordance with the present invention will be described in greater detail in the following disclosure, with reference to the attached drawings.